The nuclear-armed country stages military parades to mark important holidays and events that feature thousands of goose-stepping troops followed by a cavalcade of armoured vehicles and tanks and culminating with the key missiles Pyongyang wants to display.

Observers closely monitor these events for clues on North Korea's latest weapons development.

Monday's parade to celebrate the 90th anniversary of the founding of the Korean People's Revolutionary Army began at around 10 pm local time (1300 GMT) at the Kim Il Sung Square in Pyongyang, the source said.

It was widely expected to showcase the North's most sophisticated weaponry including the "monster" Hwasong-17 ICBM as well as hypersonic and submarine-launched ballistic missiles.

North Korea has held three nighttime military parades in recent years, with state media only reporting on the events the next day. As of Monday night, there were no reports on the latest parade.

But specialist service NK News said at least a dozen "illuminated objects" were spotted over central Pyongyang late on Monday night in a possible indicator of a military parade.

North Korea had been widely expected to showcase its military strength to mark the 110th anniversary of the birth of its founder and leader Kim Jong Un's grandfather Kim Il Sung on April 15, but instead, the day was celebrated with a civilian parade.

Satellite imagery has shown continued preparations since then, with thousands of North Korean troops and scores of vehicles marching in formation at a parade training ground in Pyongyang.

The latest event was expected to be the "biggest ever military parade", involving around 20,000 troops and the North's most advanced arsenal, South Korea's Yonhap news agency reported at the weekend citing multiple unnamed government sources.

- Nuclear test -

Pyongyang has carried out more than a dozen weapons tests this year, including firing an intercontinental ballistic missile at full range for the first time since 2017.

North Korea had paused long-range and nuclear tests while Kim Jong Un met then-US president Donald Trump for a bout of doomed diplomacy, which collapsed in 2019. Talks have since stalled.

US and South Korean officials and analysts have also warned Pyongyang could resume nuclear weapons testing for the first time since 2017, citing renewed activity at its key testing site.

Satellite imagery has shown signs of new activity at a tunnel at the Punggye-ri nuclear testing site, which North Korea said was demolished in 2018 ahead of the first Trump-Kim summit.